Tillage intensity and crop rotation affect weed community dynamics in a winter wheat cropping system R. E. Blackshaw1, F. J. Larney1, C. W. Lindwall1, P. R. Watson2, and D. A. Derksen2 1Agriculture and Agri-Food Canada, Lethbridge Research Centre, PO Box 3000, Lethbridge, Alberta, Canada T1J 4B1 (e-mail:
[email protected]); 2Agriculture and Agri-Food Canada, Brandon Research Centre, PO Box 1000A, RR#3, Brandon, Manitoba, Canada R7A 5Y3. LRC Contribution No. 38701003. Received 13 February 2001, accepted 2 May 2001.
Blackshaw, R. E., Larney, F. J., Lindwall, C. W., Watson, P. R. and Derksen, D. A. 2001. Tillage intensity and crop rotation affect weed community dynamics in a winter wheat cropping system. Can. J. Plant Sci. 81: 805–813. Development of improved weed management systems requires more knowledge on how various weed species respond to changing agronomic practices. A long-term study was conducted to determine weed population responses to various tillage intensities and crop rotations in a winter wheat (Triticum aestivum L.) dominated cropping system. Weed density and species composition differed with tillage, rotation, year, and date of sampling within years. Weed community dynamics were most affected by year-to-year differences in environmental conditions, followed by crop rotation, and then tillage intensity. Russian thistle (Salsola iberica Sennen & Pau) and kochia [Kochia scoparia (L.) Schrad.] densities increased in years of low rainfall and above average temperatures. Winter annual weeds such as downy brome (Bromus tectorum L.) and flixweed [Descurainia sophia (L.) Webb ex Prantl], as well as the perennial weed dandelion (Taraxacum officinale Weber in Wiggers), increased in years where higher than average rainfall was received in fall or early spring. Continuous winter wheat facilitated a dense downy brome infestation to develop over time. Trifluralin is not efficacious on stinkweed (Thlaspi arvense L.) or Canada thistle [Cirsium arvense (L.) Scop.] and its use in canola resulted in an increase in these species in a winter wheat-canola rotation. Total weed densities were often greater in zero tillage than in either minimum or conventional tillage. Russian thistle, downy brome, kochia, and redroot pigweed (Amaranthus retroflexus L.) were associated with zero tillage while wild buckwheat (Polygonum convolvulus L.), lamb’s-quarters (Chenopodium album L.), flixweed, and wild mustard (Sinapis arvensis L.) were associated with conventional tillage. Perennials such as dandelion and perennial sowthistle (Sonchus arvensis L.) were associated with zero tillage but Canada thistle was associated with conventional tillage. Information will be utilized to implement more effective weed management programs in winter wheat production systems. Key words: Conservation tillage, fallow, multivariate analyses, weed populations, weed shifts, zero tillage Blackshaw, R. E., Larney, F. J., Lindwall, C. W., Watson, P. R. et Derksen, D. A. 2001. Modification de la dynamique de population des adventices dans un système cultural de blé d’hiver par l’intensité du travail du sol et l’assolement. Can. J. Plant Sci. 81: 805–813. L’élaboration de meilleurs systèmes de lutte contre les mauvaises herbes exige qu’on connaisse mieux la manière dont certaines adventices réagissent aux nouvelles pratiques agronomiques. Les auteurs ont entrepris une étude de longue haleine afin de déterminer la réaction des adventices à un travail du sol d’intensité variable et à divers assolements dans un système cultural où dominait le blé d’hiver (Triticum aestivum L.). Dans une année donnée, la densité et la composition des peuplements d’adventices varient avec le travail du sol, l’assolement, l’année et la date de l’échantillonnage. La dynamique de population est avant tout affectée par la variation annuelle des paramètres environnementaux, puis par la rotation des cultures et enfin par l’intensité du travail du sol. La densité des peuplements de soude roulante (Salsola iberica Sennen & Pau) et de kochia à balais [Kochia scoparia (L.) Schrad.] augmente quand il pleut peu et que les températures dépassent la moyenne. Les adventices annuelles d’hiver tels Bromus tectorum L. et le sisymbre sagesse [Descurainia sophia (L.) Webb ex Prantl], ainsi que les vivaces comme le pissenlit (Taraxacum officinale Weber in Wiggers) sont plus nombreuses quand les précipitations sont plus abondantes à l’automne ou au début du printemps. Avec le temps, la monoculture du blé d’hiver favorise une forte infestation de B. tectorum. La trifluraline reste sans effet sur le thlaspi des champs (Thlaspi arvense L.) et le chardon des champs [Cirsium arvense (L.) Scop.]. L’utilisation de cet herbicide dans les cultures de canola augmente la densité des peuplements de ces espèces dans l’assolement blé d’hiver-canola. En général, les adventices sont souvent plus nombreuses quand on ne travaille pas le sol que lorsqu’on le travaille un peu ou normalement. La soude roulante, B. tectorum, le kochia à balais et l’amarante racine rouge (Amaranthus retroflexus L.) affectionnent les champs non travaillés tandis que la vrillée bâtarde (Polygonum convolvulus L.), le chénopode blanc (Chenopodum album L.), le sisymbre sagesse et la moutarde sauvage (Sinapis arvensis L.) préfèrent les terrains remués de la manière habituelle. Les vivaces comme le pissenlit et le laiteron des champs (Sonchus arvensis L.) sont associés au non-travail du sol, mais le chardon des champs se retrouve là où on retourne la terre. Les données de l’étude serviront à élaborer des programmes de lutte contre les mauvaises herbes plus efficaces pour la production du blé d’hiver. Mots clés: Conservation du sol, jachère, analyse multivariable, population d’adventices, évolution de la population d’adventices, non-travail du sol
Abbreviations: CDA, canonical discriminant analysis; CT, conventional tillage; MT, minimum tillage; PCA, principal components analysis; ZT, zero tillage
Soil erosion in Canada during the 1980s was estimated to cost over $1 billion annually in lost soil productivity and crop yield reductions (Anonymous 1984). Crop production 805
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systems employing conservation tillage have been widely adopted by farmers to reduce these soil losses (Lafond et al. 1990; Larney et al. 1994). Growers on the Canadian prairies also are adopting more diverse crop rotations to improve soil quality, manage pests, and increase the economic return on their farms (Brandt 1992; Zentner et al. 1992). Weeds respond to changes in agronomic production practices (Wiese 1985; Froud-Williams 1988). A reduction in tillage intensity can lead to shifts in weed species and densities with increased prevalence of perennial weeds and some annual grasses (Buhler 1992; Derksen et al. 1993; Thomas and Frick 1993; Moyer et al. 1994). Cropping sequences can also affect weed population dynamics (Ball 1992; Karlen et al. 1994; Kagode et al. 1999). For example, green foxtail [Setaria viridis (L.) Beauv.] and wild oat (Avena fatua L.) often proliferate in continuous spring cereal production and downy brome (Bromus tectorum L.) is associated with winter wheat (Triticum aestivum L.) production (Blackshaw 1994; Moyer et al. 1994). Choice of crop, and the sequence in which crops are grown, dictates different herbicide use patterns that can markedly influence weed populations (Roberts and Neilson 1981; Stevenson and Johnston 1999). Knowledge of how weed communities are affected by cropping sequences and by changing tillage practices will allow farmers to better manage their existing weeds and to predict future weed infestations. A long-term experiment was initiated in the fall of 1984 at Lethbridge, Alberta to determine the effect of various winter wheat rotations and tillage treatments on crop yield (Larney and Lindwall 1994), soil quality (Larney et al. 1997), and weed infestations. Changes in weed species and density associated with these crop rotation and tillage treatments were documented from 1987 to the completion of the study in 1994. Weed responses during the first five years of the study have been previously reported (Blackshaw et al. 1994). This paper reports on weed community dynamics over the entire duration of the study and utilizes multivariate statistical analyses to discern weed species associations with the various rotation and tillage treatments. MATERIALS AND METHODS A rotation-tillage study was conducted at Lethbridge, Alberta on a calcareous Dark Brown Chernozemic clay loam soil, with a pH of 7.6, and 1.8% organic matter. The experiment was conducted under dryland conditions with the average annual precipitation over the duration of the study being 420 mm. The crop rotation treatments were: 1) winter wheat-spring canola (Brassica rapa L.), 2) winter wheat-lentil (Lens culinaris L.)/(flax (Linum usitatissimum L.), where flax replaced lentil from 1989 onward, 3) winter wheat-fallow, and 4) continuous winter wheat. The tillage treatments were a) conventional (CT), b) minimum (MT), and c) zero tillage (ZT). Both phases of the rotations were present each year and represented the main plots in a split-plot experimental design. Tillage treatments were randomized sub-plots within the main rotation plots. All treatments were replicated six times. Main plots were 18 by 40 m and subplots were 6 by 40 m.
Conventional tillage consisted of discing and rod-weeding before planting crops; during the fallow period, an initial cultivation with a 168-cm-wide Noble blade was followed by cultivation with 40-cm-wide blades as required to control weeds (two to three times). Minimum tillage consisted of one cultivation with 40-cm-wide blades and rodweeding before planting, and tillage with a 168-cm-wide Noble blade as required during the fallow period. Glyphosate at 0.42 kg ha–1 or paraquat at 0.56 kg ha–1 were applied to zero-till plots to control weeds before planting. The commercial mixture of glyphosate/2,4-D at 0.27/0.45 kg ha–1 was applied as needed to control weeds (three to four times) on ZT fallow. Winter wheat, canola, flax and lentil were sown at 60, 5, 35, and 75 kg ha–1, respectively, using a zero-till doubledisc drill with 18-cm row spacing. For winter wheat, N and P were each applied at 30 kg ha–1 with the seed and an additional 30 kg ha–1 N was broadcast in April. For canola, flax and lentil, 30 kg ha–1 of N was broadcast before seeding and 8 and 35 kg ha–1 of N and P, respectively, were placed with the seed. Carbofuran granules at 0.27 kg ha–1 were mixed with canola to control fleabeetles (Phyllotreta spp.). If needed, chlorpyrifos at 0.5 kg ha–1 was applied to winter wheat in the fall to control Russian wheat aphid (Diuraphis noxia Mordvilko). Trifluralin was applied at 0.8 kg ha–1 in the spring before planting lentil or canola. In the CT and MT plots, trifluralin was incorporated to a soil depth of 7 cm with a field cultivator; in the ZT plots incorporation was limited to the soil disturbance caused by the seed drill. A commercial mixture of bromoxynil/MCPA at 0.28/0.28 kg ha–1 was applied in early May in winter wheat. Sethoxydim at 0.25 kg ha–1 tank mixed with the mixture of bromoxynil/MCPA at 0.28/0.28 kg ha–1 was applied to flax when it was 8 to 10 cm tall. Sethoxydim at 0.25 kg ha–1 was applied at the four leaf stage of canola. Crops were windrowed at maturity and threshed with a combine equipped with a straw spreader to evenly distribute crop residue over the plot area. Weeds were counted by species in 12 randomly chosen 0.25-m2 quadrats in three of the six replicates (always replicates 1, 4 and 5) in early May, in mid-June (prior to postemergence herbicides) in the spring-planted crops, and in late October in winter wheat in every year of the study. The only exception was October of 1990 when weeds were not counted due to early snowfall. Data were initially subjected to ANOVA with appropriate error terms used for this split-plot design. The main effects of crop rotation and tillage intensity and their interaction significantly affected weed density in most cases. Thus, to gain an overview of the data, weed density means and their standard errors were calculated and presented for the main effects and their interaction. Multivariate analyses of weed community composition were conducted using principal components analysis (PCA) and canonical discriminant analysis (CDA) in SAS (SAS Institute, Inc. 1989). PCA may be best described as a rigid rotation of axes about its origin. After rotation, the first axis accounts for the greatest amount of variance. The second, and higher axes, account for the greatest amount of variance not accounted for by previous
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Table 1. Mean density and frequency data for weed species over the study period of 1987 through 1994 for assessments taken in May, June, and October z May (n = 288) Bayer code AMABL AMARE BROTE BRSRA CAPBP CHEAL CHEGL CIRAR DESSO KCHSC LENCU LINUS MALPU POLCO SASKR SETVI SINAR SOLTR SONAR TAROF THLAR TRZAS
Scientific name Amaranthus blitoides S. Wats. Amaranthus retroflexus L. Bromus tectorum L. Brassica rapa L. Capsella bursa-pastoris (L.) Medicus Chenopodium album L. Chenopodium glaucum L. Cirsium arvense (L.) Scop. Descurainia sophia (L.) Webb. ex Prandt Kochia scoparia (L.) Schrad. Lens culinaris L. Linum usitatissimum L. Malva pusilla SM. Polygonum convolvulus L. Salsola iberica Sennen & Pau Setaria viridis (L.) Beauv. Sinapis arvensis L. Solanum triflorum Nutt. Sonchus arvensis L. Taraxacum officinale Weber in Wiggers Thlaspi arvense L. Triticum aestivum L.
Common name
Density # (plants m–2) plots
Jun (n = 135)
Oct (n = 252)
% Density # freq (plants m–2) plots
% Density # freq (plants m–2) plots
% freq
Prostrate pigweed Redroot pigweed Downy brome Volunteer canola Shepherd’s-purse
